In order to make use of biologically active compounds it is often desirable to formulate them with inert carriers, for instance, organic solvents. The solubility of the active compound in its carrier determines the strength of the formulation. This formulation, whether a true solution or a dispersion, should be stable under normal conditions of shipping and storage and preferably should remain liquid at temperatures down to about 0.degree. C.
It may also be advantageous to include more than one biologically active compound in a given formulation. The combination allows the realization of the beneficial effect of the components from a single application.
A particularly attractive herbicide for the control of weeds in connection with crops is 3-methyl-thio-4-amino-6-tert. butyl-1,2,4-triazin-5-one of the formula ##STR1## and commonly known as metribuzin. The preparation of the compound of formula I as well as herbicidal compositions containing this compound as an active ingredient are described in U.S. Pat. No. 3,961,936 Unfortunately, this compound has a high melting point (about 120.degree. C.) and limited solubility in common organic solvents such as alkyl benzenes.
U.S. Pat. No. 3,986,862 suggests that metribuzin be combined with 2-chloro-N-(2,6-diethyl-phenyl)-N-methoxymethylacetamide of the formula ##STR2## and commonly known as alachlor. The combination is reported to interact synergistically with chlorobenzene to allow higher concentrations of the active ingredients in stable solutions.
It is an object of the present invention to render metribuzin more amenable to formulation with inexpensive nonhalogenated diluents and inert carriers. It is also an object to combine metribuzin with another herbicidally active compound. Finally, it is an object of this invention to enhance the solubility of metribuzin in alkyl benzenes.
Surprisingly, it has been found that these objects may be achieved by combining metribuzin with alachlor in the presence of alkyl benzenes.